Rotary ball valves are known for fluid flow control. They are provided along a pipeline for enabling and stopping fluid flow as required.
One of the known designs of ball valve is with two or three piece valve body structures, primarily for ease of assembling and disassembly. Such designs are prone to leakage at valve body joints. Also, valve body joints are the weakest areas which decide the capacity of such ball valves for withstanding in-line fluid pressure stresses. More importantly, such valves are not conducive to repair and maintenance and need to be removed from pipe line, thus increasing downtime and cost of maintenance.
Top entry ball valves are generally made of single piece valve body within which is movably located a ball member having a through passage. The ball member has lower end trunnion housed in the valve body and upper trunnion housed in the valve cover. The stem is connected to the ball member in any suitable manner. Trunnion mounted ball valves are provided with floating ball seat assemblies which are movable linearly within the valve body and which establish sealing engagement with the spherical sealing surface of the ball member. The ball seats have tubular grooves to receive the soft seals. Top entry trunnion type ball valves have been in use for a considerable period of time and are considered to minimize many of the undesirable features of ball valves having two or three piece sectioned valve body structures. The advantages of top entry ball valves include a one piece valve body structure to withstand line stresses with no valve body joints for possibility of leakage. Also they are not necessarily required to be removed from the pipe line for maintenance.
In trunnion mounted ball valves, two ball seats are oppositely located in ball seat recesses in the valve body at each side of the ball member, being axially aligned with ball and valve body flow passages. The ball seats are preloaded against the sealing surface of the valve ball by the force of various types of springs positioned behind the ball seats. This spring preload is required to create initial sealing contact of the ball seats against the ball member for further line pressure responsive ball seat sealing. The springs are housed in the Seat retainer which is housed in the cylindrical recess in the valve body.
Because of the ball seats are under spring preload condition, it is necessary to provide some means to retract the ball seats to create and maintain the clearance between the ball seats and the ball member so that the ball member can be easily inserted or removed from the assembly without damaging the spherical sealing surfaces of the ball seats and the ball member by any obstructing conditions.
There are disclosures for easy removal and insertion of ball member and other internal parts for on-site and in-line maintenance of top entry trunnion mounted valves.
U.S. Pat. No. 4,637,421A discloses an in-line repairable top entry ball valve. The ball/ball seat spacers form sealing surfaces at one axial end for sealing engagement with the ball member and sealing surfaces at the opposite axial end for sealing engagement with the ball seats and in spherically concentric relation with the ball to thus permit installation and removal of the ball/ball seat spacers in an arcuate motion about the spherical surface of the ball. When ball/ball seat spacer is removed, a gap created between the ball seat and the ball, and the ball member can be removed. After repair and or maintenance of inner parts of valve, the ball is inserted and the gap between the ball seat and the ball is again filled by inserting the ball/ball seat spacer.
U.S. Pat. No. 4,175,577 discloses means and method for in-line removal of ball seats in ball valves, which includes a separate cam tool inserted between the ball and the ball seats after removal of the cover plate. The cam tool is positioned within the bore of the ball which has been partially rotated from the full open position, and upon a return rotation of the ball with the cam tool therein to a full open position an adjacent spring urged ball seat is cammed away from the ball to a retracted position. A ball seat retainer is then actuated to hold the ball seat in the retracted position. The cam tool is then utilized in a similar manner to cam the other opposite ball seat in retracted position. The ball may then be removed with the ball seats for replacement or repair as desired.
U.S. Pat. No. 4,388,945 A discloses Valve assembly and disassembly device. In one embodiment a conical ended pin is described which causes camming surface between the pin and ball seat. After removal of the top cover, the conical ended pin is inserted in indexed holes in the housing and as pin advances in the gap between the ball and the ball seat, the ball seat retracts against spring force. In another embodiment, the ends of the pins are teardrop shaped. After the pins are inserted, they are rotated 90° causing ball seat retraction by the larger diameter of the pin. The indexing holes for the insertion of pin are made in the interior part of the housing needing no puncturing of housing or cover.
A similar ball seat retraction is evidenced in U.S. Pat. No. 4,390,039 titled “Valve assembly and disassembly device”.
U.S. Pat. No. 4,566,482A/EP 0207755 A2 titled “Top entry trunnion ball valve” discloses ball seat retraction by camming between the ball seat and the bearing seat. Rotation of a bolt of lower trunnion moves the bearing seat upward direction resulting in retracting movement of both ball seat members by their interacting with cam surfaces of the bearing seat. The bearing seat then occupies place between the ball seats and the ball seats stay locked in retracted position.
In U.S. Pat. No. 4,262,691 A entitled “Cam means for ball valve ball seats” the camming surfaces are formed between the cam pins directly mounted on the ball member and the ball 1 seat. A removable stop engages and blocks rotation of the ball member past its fully opened and fully closed positions and the cams engage the seat rings only after the stop is removed and the ball member is rotated past its normal stroke and beyond fully opened or fully closed positions.
U.S. Pat. No. 6,681,793 B2/U.S. Pat. No. 3,934,606 disclose another Ball seat construction. Camming surfaces are formed between the ball seat flange and the plate which are coupled to top and bottom shoulders of the trunnion of ball member to fully retract the spring-biased valve ball seat. The retraction tool can be inserted to hold the ball seats in position. For insertion of the holding tool access is provided by creating an additional opening on the main housing.
U.S. Pat. No. 3,934,606A titled “Cam locked ball valve” discloses a trunnion mounted ball valve with cam plates mounted on the stem axis. Cam followers on the ball seats engage in cam slots in the plates to move the ball seats positively into firm engagement with the ball at the open and closed positions thereof and retract them free of the ball as it is moved between those positions. The ball seats slide axially in slide rings which are threaded into the valve body around the flow passage. The valve ball, ball seats, and slide rings may be removed as a unit through the valve top opening.
U.S. Pat. No. 3,171,429, titled “Valve with spherical plug” discloses a ball valve in which cams are positioned on the ball member to engage bushings or carriers for the ball seats.
While there are several other disclosures to retract the ball seat and retain in retracted position, there is scope to simplify the retraction method for top entry trunnion mounted rotary valves in construction and cost, with reduced possibilities of mal function, damage to ball member and inadvertent locking, and avoid additional weaknesses like associated leakage paths.